package org.jiajie.coffeecodes.algorithm;

/**
 * 雪花算法
 * Twitter的SnowFlake算法，使用SnowFlake算法生成一个整数，然后转化为62进制一个短地址URL
 * @author jay
 */
public class SnowFlakeShortUrl {

    /**
     * 起始的时间戳
     */
    private final static long START_TIMESTAMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    /**
     * 序列号占用的位数
     */
    private final static long SEQUENCE_BIT = 12;
    /**
     * 机器标识占用的位数
     */
    private final static long MACHINE_BIT = 5;
    /**
     * 数据中心占用的位数
     */
    private final static long DATA_CENTER_BIT = 5;

    /**
     * 每一部分的最大值
     */
    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_DATA_CENTER_NUM = -1L ^ (-1L << DATA_CENTER_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT = SEQUENCE_BIT;
    private final static long DATA_CENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTAMP_LEFT = DATA_CENTER_LEFT + DATA_CENTER_BIT;

    /**
     * 数据中心
     */
    private long dataCenterId;
    /**
     * 机器标识
     */
    private long machineId;
    /**
     * 序列号
     */
    private long sequence = 0L;
    /**
     * 上一次时间戳
     */
    private long lastTimeStamp = -1L;
    
    private long getNextMill(){
        long mill = getNewTimeStamp();
        while (mill <= lastTimeStamp) {
            mill = getNewTimeStamp();
        }
        return mill;
    }

    private long getNewTimeStamp() {
        return System.currentTimeMillis();
    }

    /**
     * 根据指定的数据中心ID和机器标志ID生成指定的序列号
     *
     * @param dataCenterId  数据中心ID
     * @param machineId 机器标志ID
     */
    public SnowFlakeShortUrl(long dataCenterId, long machineId) {
        if (dataCenterId > MAX_DATA_CENTER_NUM || dataCenterId < 0 ) {
            throw new IllegalArgumentException("DataCenterId can't be greater than MAX_DATA_CENTER_NUM or less than 0!");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("MachineId can't be greater than MAX_MACHINE_NUM or less than 0!");
        }
        this.dataCenterId = dataCenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     * @return next id
     */
    public synchronized long nextId(){
        long currTimeStamp = getNewTimeStamp();
        if (currTimeStamp < lastTimeStamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }
        if (currTimeStamp == lastTimeStamp){
            // 相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            // 同一毫秒的序列数已经达到最大
            if (sequence == 0L){
                currTimeStamp = getNextMill();
            }
        } else {
            // 不同毫秒内，序列号置为0
            sequence = 0L;
        }
        lastTimeStamp = currTimeStamp;
        return (currTimeStamp - START_TIMESTAMP) << TIMESTAMP_LEFT //时间戳部分
                | dataCenterId << DATA_CENTER_LEFT                  // 数据中心部分
                | machineId << MACHINE_LEFT                         // 机器标识部分
                | sequence;                                         // 序列号部分
    }

    public static void main(String[] args) {
        SnowFlakeShortUrl snowFlake = new SnowFlakeShortUrl(2, 3);
        System.out.println(" " + (1 << 4));
        for (int i = 0; i < (1 << 4); i++) {
            // 10进制
            System.out.println(snowFlake.nextId());
        }
    }
}
